I've made some changes after a test run... Changed two Royal Throne Rooms for Two Canterlot; removed the red part of the mana (Mountains, sweet Apple Acres and AJ as well The Stare) and added more green/white creatures (Angel and Octavia) and also two more Elements (Loyalty) to increase the times Celestia places her three pegasus tokens.

Derpy Hooves serves as a wall and helps to diminish the effect of Canterlot and Everfree Forest.

Opal with the Gala dress is useful to get rid of small annoying creatures. Until Rarity and Fluttershy come along to increase the ammount of attacking creatures. Once it comes I attack with a horde of Tokens (Pegasus and Parasprites) leaded by Derpy. With Everfree granting Trample and Cosmic Conflict boosting my creature's powers.

The idea is to create as many Parasprite and Pegasus tokens to protect and then attack with an overwhelming force, hence the three Depry Hooves and the Four Canterlot as they create the tokens. Poison Joke and Vegeance of the Sun takes care of annoying creatures as Zekora speeds ups the mana production and stalls the creatures as well.

Sweetie Belle and oplaescence are in there to protect and give time until the big ponies come to the field.

Fluttershy is there to gain life as Rarity also helps stall the opponent. So at the end if anything else goes as well, The stare handes me over the rival's creatures and then launche the final offensive.

It should be noted that the last ability simply states "counters", not "muffin counters". Go go 10 +1/+1 counters for a 21/21 Derpy Sure it's easier to go with muffins, but there's probably some tricks to get the count to 10 sooner.

I like counters too, but the problem with having too many is that it adds a whole lot of clutter to a board. One possible way to get rid of the counters here is to just have the last ability count the number of Parasprites you control.

Then you can add, "This ability can only be played if Derpy Hooves has fewer than 10 muffin counters". Also, the way it is now, it can be at 10 counters and then they proliferate it to 11 and it reverts to the 1/1.